1. Field of the Invention
The present invention relates to a method of forming a lamination film pattern and an improved lamination film pattern, and more particularly to a method of forming a metal lamination film pattern which comprises a first metal film comprising a refractory metal such as chromium or a chromium alloy, and a second; metal film overlying the first metal film and comprising aluminum or an aluminum alloy, wherein the method is free from any inhibition to etching for the first metal film of chromium or the chromium alloy, and also free from any peeling of a resist film from the metal lamination film due to over-time etching process.
2. Description of the Related Art
All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will, hereby, be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
A liquid crystal display has a plurality of switching devices, each of which comprises a thin film transistor (TFT), wherein any wiring delay appearing on a scanning line or a signal line causes a writing or crosstalk problem. In order to avoid this problem, the liquid crystal display, particularly to a large-scale and high-definition liquid crystal display, uses a low-resistive wiring for the scanning line or the signal line. In general, the low resistive wiring may comprise aluminum or an aluminum alloy. In the technical field of the liquid crystal display, in order to ensure a desired ohmic contact with a semiconductor layer and a transparent conductive film. The low resistive wiring may comprise a lamination structure of an aluminum or aluminum-alloy film and a refractory metal film. Typically, for example, the low resistive wiring may, comprise a double-layered structure of an aluminum layer and a refractory metal layer overlying the aluminum layer. The low resistive wiring may also comprise another double-layered structure of a refractory metal layer and an aluminum layer overlying the refractory metal layer. The low resistive wiring may also comprise a triple-layered structure of a first refractory metal layer, an aluminum layer overlying the first refractory metal layer, and a second refractory metal layer overlying the aluminum layer.
Japanese laid-open patent publication No. 4-155315 discloses a conventional method of forming an. Al/Cr lamination wiring, wherein an aluminum film overlies a chromium film. This method is applied to a thin film transistor array substrate. FIGS. 1A through 1D are fragmentary cross sectional elevation views illustrative of an Al/Cr lamination wiring over a substrate in sequential steps involved in the conventional method of forming the Al/Cr lamination wiring.
With reference to FIG. 1A, a first metal film 102 of chromium is formed over a substrate 101. A second metal film 103 of aluminum is then formed over the first metal film 102 of chromium, A desired resist pattern 104 is formed over the second metal film 103 of aluminum. A first etching process is taken place by using a first etchant and the resist pattern 104 as an etching mask for selectively etching the second metal film 103 of aluminum.
With reference to FIG. 1B, a second etching process is taken place by using a second etchant and the resist pattern 104 as the etching mask for selectively etching the first metal film 102 of chromium.
With reference to FIG. 1C, a third etching process as a side etching process is taken place by using the first etchant and the resist pattern 104 as the etching mask for selectively etching the side of the second metal film 103 of aluminum, so that the etched side edge of the second metal film 103 of aluminum is retracted by at least 0.5 micrometers from the side edge of the first metal film 102 of chromium.
With reference to FIG. 1D, the resist pattern 104 as used is then removed. Subsequently, a conductive film such as a pixel electrode is then formed, which extends over the second metal film 103 of aluminum and the substrate 101.
The third etching process as the side etching process is taken place in order to improve a step-coverage of the conductive film which extends over the second metal film 103 of aluminum and the substrate 101, resulting in improves in the yield and the quality of the thin film transistor (TFT) substrate.
The present inventors had experimentally confirmed the fact that the above-described conventional method of forming the lamination film pattern has the following disadvantages.
The rate of the second etching process is extremely low due to an inhibition to the second etching process for the first metal film 102 of chromium. Taking place the second etching process for a relatively long time period causes that an etchant for the second etching process be infiltrated into an interface between the resist pattern 104 and the second metal film 103 of aluminum, whereby the resist pattern 104 is peeled to contaminate an etching apparatus.
The present inventors had also estimated that the reason for the inhibition to the second etching process for the first metal film 102 of chromium is that a hetero-metal-contact-potential-difference between the first metal film 102 of chromium and the second metal film 103 of aluminum causes the etchant for etching the first metal film 102 of chromium to undesirably etch the second metal film 103 of aluminum.
In the above circumstances, the developments of a novel method of forming a lamination film pattern and of an improved lamination film pattern free from the above problems are desirable.